A combustion section of a gas turbine generally includes a plurality of combustors that are arranged in an annular array around an outer casing. Pressurized air flows from a compressor to each combustor. Fuel from a fuel supply is mixed with the pressurized air in each combustor to form a combustible mixture within a combustion chamber of each combustor. The combustible mixture is burned to produce hot combustion gases having a high pressure and high velocity. The combustion gases are routed through a hot gas path towards an inlet of a turbine. Thermal and kinetic energy are transferred from the combustion gases to the turbine to cause the turbine to rotate, thereby producing mechanical work.
Many high efficiency gas turbines, particularly in the power generation industry, are fueled by a gaseous fuel such as natural gas and/or a liquid fuel such as diesel or kerosene. Typically, the natural gas is mixed with the pressurized air from the compressor to provide a combustible mixture to the combustion chamber for combustion. The liquid fuel is used for diffusion combustion during turndown and or part load operation of the gas turbine. However, some gas turbines may operate solely on the liquid fuel.
Natural gas and/or liquid fuel generally require a reliable supply source and an adequate delivery system that extends between the source and the gas turbine facility. If either the source or the delivery system are interrupted and/or compromised such as by equipment failure or excess demand, the gas turbine will have to be taken offline until the fuel supply issue can be resolved. As a result, many gas turbine operators utilize a backup fuel supply system that is fluidly connected to the combustors.
Typically, a backup fuel supply system relies on a liquid fuel such as kerosene or diesel to fuel the combustors. However, various alternative light and highly volatile liquefied fuels such as propane, butane, and variety of their mixes known as liquefied petroleum gas or LPG fuels are also suitable as alternative backup liquid or liquefied fuels for gas turbines. In addition, various other fuels with similar thermodynamic properties are also suitable as alternative backup fuels to the more commonly used kerosene and/or diesel such as pentane, methanol, ethanol and dimethyl ether (DME).
In many instances, these alternative liquefied fuels are produced as byproducts of various industrial processes at industrial facilities such as refineries, chemical plants and/or liquefied natural gas processing plants. As a result, these alternative liquefied fuels are readily available and can be collected and stored for later use onsite or routed to an offsite location, thereby reducing the operator's costs to operate the backup fuel supply system. In addition, the alternative liquefied fuels generally have higher specific caloric values and are generally cleaner to burn than the commonly used liquid fuels such as kerosene and diesel fuels.
In order to use the alternative liquefied fuels as a backup fuel in either a gaseous or liquid fuel combustor, the alternative liquefied fuels must be vaporized and mixed with a diluent and/or a carrier gas such as air to produce a gaseous fuel mixture. The gaseous fuel mixture may then be injected into the combustor where it is used in the same fashion as in a natural gas combustor. The process of vaporization of the alternative liquid/liquefied fuels retains low emissions associated with combustion of gaseous fuel and reduces or eliminates the need for additional combustion hardware required to burn the more commonly used liquid backup fuels (kerosene or diesel) while also realizing the benefits of using the alternative liquefied fuels to fuel the combustors.
Vaporization system efficiency, capital and/or operating costs continue to drive operators and designers to seek new and improved backup fuel systems that utilize alternative fuels such as the liquefied fuels described above. Therefore, an improved backup fuel system that allows operators to use the alternative liquefied fuels would be useful.